Chap_47.doc

 Conservation biology – an applied scientific discipline devoted to preserving the
diversity of life on Earth
■ modern conservation biology is supported by and integrated with other
scientific disciplines
■ humans study the full array of goods and services that humans derive from
species and ecosystems
■ it's a normative discipline – embraces certain values and applies scientific
methods to the goal of achieving these values
■ motivated by belief that preservation of biodiversity is good and that its loss
is bad
 Conservation biology is guided by 3 basic principles:
■ Evolution is the process that unites all of biology
■ The ecological world is dynamic
■ Humans are a part of ecosystems
 early photosynthetic prokaryotes and eukaryotes generated oxygen, making
Earth's atmosphere unsuitable for anaerobic organisms
 plants accelerated weathering of the rocks, gaining access to rock-bound nutrients
 endemic species – species that are found nowhere else
 humans have been exterminating species for 1000s of years due to over-hunting
 People value biodiversity because:
■ Humans depend on other species for food, fiber and medicine
■ Species are necessary for the functioning of ecosystems and the many
benefits and services those ecosystems provide to humanity
■ Human derive enormous aesthetic pleasure from interacting with other
species
■ Extinctions deprive us of opportunities to study and understand ecological
relationships among organisms
■ Living in ways that cause extinction of other species raises serious ethical
issues because species are judged to have intrinsic value
How Do Biologists Predict Changes in Biodiversity?
 To preserve Earth's biodiversity, we need to both maintain the processes that
generate new species and provide conditions that will keep extinction rates no
higher than typical levels
 4 reasons that scientists cannot predict the number of extinctions that will occur:
■ We do not know how many species live on Earth
■ We do not know where species live
■ It is difficult to determine when a species actually becomes extinct
■ We do not know what will happen in the future
 North America's largest woodpecker, the ivory-billed pecker, was considered
extinct for 60 years until recently where there have been claimed sightings
 Species-area relationship – a well-established mathematical relationship between
the size of an area and the number of species it contains
 conservation biologists have measured the rate at which species richness
decreases with decreasing habitat patch size
■ found that a 90% loss of habitat will result in the loss of half the species that
live in and depend on that habitat
■ current loss of tropical evergreen forests (the most species-rich biome) is 2%
per year
 conservation biologists develop statistical models that incorporate information
about a population's size, its genetic variation, morphology, physiology and behaviour of its members to estimate risks of extinction
■ Endangered species – in imminent danger of extinction in all or a specific
part of their range
■ Threatened species – likely to become endangered in the future
■ rarity is not a cause for concern
 species whose populations are suddenly shrinking rapidly are usually at high risk
 species with special habitat or dietary requirements are more likely to become
extinct
 populations with a few individuals confined to a small range can be easily
eliminated by local disturbances
 the golden toad in Costa Rica became extinct due to climate warming
What Factors Threaten Species Survival?
 habitat loss is most important cause of species endangerment in the U.S.
Especially for species in freshwater
 Fragmentation – as habitats are progressively lost to human activities, the
remaining patches become smaller and more isolated
■ small patches cannot maintain populations of species that require large
areas
 Edge effects - the fraction of a patch that is influenced by factors originating
outside it increases rapidly as patch size decreases
■ species from surrounding habitats colonize on the edges of patches to
compete with or prey on species living there
■ species disappeared from isolated patches when the surrounding forest was
cut
■ species that are lost from small habitat fragments are unlikely to become
reestablished there because dispersing individuals are unlikely to find
isolated fragments
■ a species may persist in a small patch if it is connected to other patches by
corridors of habitat through which individuals can disperse
 Invasive – when species spread widely and become unduly abundant, often at a
cost to the native species of the region
 most introduced species are imported without their natural enemies, while native
plants must devote considerable energy to defending themselves against the
native herbivores
■ invasive plants generally have high rates of growth and reproduction
because they spend less energy in producing defensive compounds
■ introduced pathogens have destroyed whole populations of several eastern
North American forests
■ disease outbreaks usually leave no traces in the fossil record
 due to human activities, average temperatures in North America will increase
about 2-5 C
 organisms that are able to disperse easily may be able to shirt their ranges as
rapidly as the climate changes provided that appropriate habitats exist in new
areas
 ranges of species with sedentary habits are likely to shift slowly
 if Earth's surface warms as predicted, new climates will develop and existing
climates will disappear
■ new climates are certain to develop at low elevations in the tropics
 if warming of oceans continues about 40% of coral reefs are likely to be killed ■ reefs adjacent to cool, upwelling waters and reefs in cloudy waters have
relatively low temperatures and are healthy
What Strategies Do Conservation Biologists Use?
 Protected areas – an important component of efforts to preserve biological
diversity
■ preserve habitats while preventing the human exploitation of the species
living there may serve as nurseries from which individuals disperse into
exploited areas
■ The fundamental requirement for the conservation of biological diversity is
the in situ conservation of ecosystems and natural habitats and the
maintenance and recovery of viable populations of species in their natural
surroundings – United Nations Convention
■ How to select areas being protected
 Species richness – the number of species living in an area
 then umber of endemic species
 biodiversity “hotspots” occupy 15.7% of Earth's land surface but are home to 77%
of Earth's terrestrial vertebrate species
■ hotspots are also regions of high human populations whee habitat
destruction is a major problem
 WWF identified 200 regions of great conservation importance, including marine
areas, tundra, boreal forests and deserts
 conservation biologists have analyzed distributions of animals and have identified
595 centers of imminent extinction
■ the sites harbor 794 species judged to be at serious risk of extinction
 Restoration ecolog